Solid changes, for the most part, though still a few problems. You asked if I'd respond to your revisions, so here we go:
Scavenger – Action – 0$
“Choose one: gain a card costing up to 5$ from the trash pile; or gain a Copper, putting it into your hand.”
to...
Scavenger – Action – 0$
“Choose one: gain a card costing up to 2$; or gain a card costing up to 5$ from the trash pile.”
I actually like this about equally either way. Ill-Gotten Gains shows how much gaining a Copper to hand might actually be a good thing. The second version is quite different and depends a lot on whether there are any $2 cantrips. If not, it's an Estate-gainer in the end game. I still don't like trash-retrievers on principle, but having an alternative option makes it playable.
^i liked this card before, but i'm thinking it will see more use now.
Rats – Action – 1$
+1 Card per Rats in play, +1 Action per Rats in play, “If there are 2 Rats in play, immediately put them into your discard pile and gain a Curse."
At $1, this card shouldn't be powerful, but it's
really not powerful. If you have just one, all it does is replace itself, exactly as if you hadn't bought it at all. If you have two, you get a level 2 City effect and get cursed. I can't imagine when you'd ever want these. If you took the cursing out, it's probably balanced at $1, but since your average income per turn starts at $3.5 and goes up from there, when would you ever want to burn a buy on one, let alone two?
^this card was just not getting picked. this is a more tempting, and more dangerous buy. i didn't like the 'targeting' either. i also think this as an improvement flavor-wise. i really like the 1$ price because it feels like a discount, when it's usually not, and thus makes the Rats seem 'smaller.'
Plague Doctor – Action-Reaction – 3$
+2$ / “When you would gain a card, you may set this aside from your hand. If you do, instead, gain a Copper; then at the start of your next turn, +1 Action and return this to your hand.”
This is only useful as a response to Cursing attacks, and then Moat/Lighthouse/Watchtower/Trader are still vastly superior. Gaining Copper is almost always a bad thing, so exchanging a Curse for a Copper is barely an improvement. You'd rather not gain anything. So on non-cursing boards, this is strictly worse than Silver; on cursing boards, I'd still pass this up, preferring to take the Curses rather than clog my deck up with this card.
That's the problem with the base treasure cards -- the scale is so granular. Copper is terrible, Silver is okay, and Gold is fantastic. There's nothing in between: if you want to have a good inexpensive card that helps you gain lots of one of them, Silver is the only one of the three that works.
Missionaries – Action – 3$
+1 Card, +1 Buy, “You may immediately look through your discard pile, reveal up to 2 cards with a cost of 0 from it, and trash them.”
^this card needed some nerfing, but i like it. i also needed more + Buys and less + Cards in the deck to encourage using the cheaper cards.
I like the reasoning. This card seems fine.
Inheritance – Action – 4$
+2 Cards, +2$, “When you would discard this from play, instead, you may put this on the bottom of your deck.”
to...
Inheritance – Action – 4$
“Immediately put your deck into your discard pile.” +1 Card, +2$
Seems perfect now. Nice idea.
Relief – Treasure – 5$
-1$, +1 Buy, “When you play this, reveal your hand. +1$ for every card with a cost of 0 you have in your hand or in play.”
to...
Relief – Treasure – 4$
+0$, +1 Buy, “When you play this, count the cards in the trash pile. If there are no cards in the trash pile, gain a Silver, putting it into your hand. Otherwise, +1$ for every 2 cards in the trash pile (rounded down).”
This seems like a very strange hybrid. I don't really understand the synergy between the different pieces. Also note that while some games have 0 cards in the trash (which you've accounted for), some games have
dozens of cards in the trash pile, which would make this a powerhouse of epic proportions. It's good if a card is good sometimes and bad other times, but the variance on this is huge.
Morgue – Action – 5$
+4 Cards, “Each player (including you) may trash a card from his hand.”
to...
Morgue – Action – 5$
+4 Cards, “Gain a curse."
Much better but still a problem. For one thing, cursing is harmful enough that I'd want to see +5 Cards or drop the price. But never mind: the main problem is that once the curses run out, they become juggernauts. This is a fairly exhaustively discussed in other threads in this subforum (and has an entry in my fan card guide). The easiest fix is "Gain a curse. If you do...." Alternately, invent a "curse token," something that's worth -1 VP at the end of the game but is unlimited and doesn't go into your deck. If you do that, note that curse tokens are a LOT less harmful (usually) than curse cards, so you have to take that into account when adjusting the power level of the card as a whole.
Sewers – Action-Victory – 5$
“Worth 1 Victory for every 3 cards with a cost of 0$ in your deck (rounded down).” / “Trash a card from your hand. Gain a number of Coppers equal to its cost in coins."
Now that's synergy. I like that. I'd suggest trying a cost of $4, not for power-level reasons but just because that makes it a much easier card to try to race for when you're playing a Copper strategy, as you would be if you played this card at all.
